In general, the electrospinning is used to produce fibers having a diameter of several nanometers by using various kinds of polymers, i.e., polymer melt, polymer solution, etc.
A nanofiber gives various physical properties, since the fiber shows a very high area-to-volumn ratio in comparison with the conventional fiber. A web composed of these nanofibers is a material of porous membrane, which is useful in various fields such as various filters, a dressing for medical treatment and an artificial support.
In the conventional electrospinning, a fiber is manufactured by discharging solution less than several grams per second from one or a small number of nozzles, which is not economical due to the slow producing rate.
U.S. Pat No. 4,323,525 discloses a technique related to the electrospinning, in which a tubular product is made by electrostatically spinning a fiber-forming solution on a rotating mandrel charged at −50 kV by three grounded syringes. However, this technique is not suitable for manufacturing many nanofibers because of the restriction of a shape and number of the spinning nozzles being adapted. In addition, since the technique is limited to manufacturing tubular products, it is difficult to continuously manufacture multi-purpose planar webs.
Until now, various electrospinning nozzles have been suggested in the following documents: a syringe needle [J. M. Deitzel, J. D. Kleinmeyer, D. Harris, N. C. Beck Tan, Polymer 42, 261-272 (2001)]/[J. M. Deitzel, J. D. Kleinmeyer, J. K. Hirvonen, N. C. Beck Tan, Polymer 42, 8163-8170(2001)], a capillary metal tube [Y. M. Shin, M. M. Hohman, M. P. Brenner, G. C. Rutledge, Polymer 42, 9955-9967(2001)], a capillary glass [J. Doshi, D. H. Reneker, Journal of Electrostatics 35, 151-160(1995)], etc.
As described above, the problem caused by a small number of the spinning nozzles can be overcame by using many nozzles. However, using many nozzles causes the discharge of solvent to be not easy and makes the stream of solution be irregular due to the repulsion between charged filaments.
On the other hand, Korean Laid-open Pat. Publication No.2002-0051066 discloses “Apparatus for producing a polymer web”, which includes a base having an inlet pipe for allowing melted polymer materials to pass through, a base conductor board attached on the lower surface of the base for transferring electric charges, at lease one nozzle mounted to nozzle taps formed on the base conductor board for discharging the polymer material, a charge distribution board mounted to a lower portion of the base conductor board, and a conductor board mounted to a lower portion of the charge distribution board.
Since all conductor boards for transferring electric charges are exposed and a separate conductor board is located between the base conductor board and the collector, this apparatus disadvantageously forms too strong and unnecessary electric fields between the spinning part and the collector, causing the discharge of solution not regular when many spinning nozzles are configured.
In addition, the strong electric field causes formation of agglomeration at ends of some spinning nozzles when the solution is discharged, thereby resulting that webs unclear or having irregular diameters are manufactured.
On the other hand, if the apparatus is composed of multiple nozzles, the stream of solution deviates from its path due to the repulsion between the filaments discharged with the same polarity, so the stream may not be appropriately induced to a correct location on the collector.